A light diffusing sheet comprising a diffusing agent such as silica, glass, or alumina dispersed in a base material of a transparent or semi-transparent thermoplastic resin is known for use in transmission projection screens, illumination and the like.
The above light diffusing sheet has been extensively put to practical use by virtue of its easy production and advantageous cost effectiveness. In this light diffusing sheet, however, when the amount of the diffusing agent used is increased for large viewing angle provision purposes in transmission projection screen applications, a significant light quantity loss or a deterioration in transparency and image resolution often occurs.
Japanese Patent Laid-Open No. 120702/1990 proposes, as one means for solving the above problem, a light diffusing sheet using a light diffusing agent in which the refractive index of the outermost edge part and the refractive index of the center part of the light diffusing agent have been specified.
The claimed advantage of the technique described in Japanese Patent Laid-Open No. 120732/1990 is to produce a light diffusing sheet which can provide images having excellent transparency, is low in light quantity loss of a light source, and can provide good light diffusing characteristics.